Semiconductor devices are tested during fabrication to detect defects and demonstrate satisfactory performance. The testing is performed on devices (also known as dies) that are formed on, for example, a silicon wafer before the devices are diced (separated from the wafer and each other). By performing such testing at various points in the fabrication process, it's possible to identify which units are good and which units are defective or potentially defective. This can result in savings in cost and time, because the defective units need not be passed through the remainder of the fabrication process and/or undergo other testing at later stages of the fabrication process.
Gate oxide integrity (GOI) is of increasing importance for device manufacturers, especially because the thicknesses of the gate oxide layers in the devices are being reduced as the devices shrink in size. Producing reliable, high-quality gate oxide layers in semiconductor devices is therefore a critical task in semiconductor fabrication, and testing is performed during fabrication to check GOI. This testing includes subjecting the gate oxide layer of each device on the wafer to a stress test in which a voltage higher than the rated voltage is applied to the gate electrode.
Electro-static discharge (ESD) is an event that sends current through a semiconductor power device. To protect against ESD, many semiconductor devices incorporate ESD protection networks directly onto each device. However, once an ESD protection network is formed on a device, it is not possible to monitor characteristics such as GOI during the fabrication process. The leakage from the ESD protection networks is greater than the voltage applied to the gate oxide layer during the stress test. In other words, the higher voltage that is supposed to be applied to the gate oxide layer in the stress test is instead dissipated through the ESD protection network. While overall device characteristics can be measured with the ESD protection network in place, characteristics related to GOI are different from the overall device characteristics.